Various technologies for identifying a one-dimensional barcode in an image are known. For example, there has been proposed such a technology, in which the entire area of image data is sequentially scanned, whereby a tentative barcode area in which black and white patterns appear alternately is extracted. Then, it is determined whether or not predetermined bar patterns exist in the tentative barcode area so as to extract a true barcode area. Specifically, a pattern of guard bars composed of two black bars and a white bar between the two black bars and a pattern of center bars composed of three white bars and two black bars between the three white bars are previously registered in a memory. It is determined whether or not the registered guard bar pattern exists at each of both ends of the tentative barcode area and the registered center bar pattern exists at the center of the tentative barcode area.